1. Field of the Invention
The present invention relates to a recording and reproducing method and an apparatus thereof for a dye-based recordable (write once read many) DVD medium which can record and reproduce information by irradiating light-beam to produce optical changes of transmission, reflectance, and others in a recording layer, and is also recordable.
2. Description of the Related Art
Development of DVD±R as a large capacity optical disc is progressing now. The element technologies for improving recording capacity are required to be developed, which include development of recording material for micronization of record-pits, introduction of image compression technology represented by MPEG2, and short-shifting of semiconductor laser wavelength which is used for reading record-pits.
As a semiconductor laser in the red wavelength region, only an AlGaInP laser diode of a 670 nm band has been commercialized so far for barcode readers or measuring instruments. However, with the densification of optical discs, red lasers have begun to be used on a full scale in the optical storage market. DVD drives have been standardized by using laser diodes of two bands of wavelengths, a 635 nm band and a 650 nm band, as light sources. On the other hand, playback-only DVD-ROM drives have been commercialized at a wavelength of about 650 nm.
Generally, in a dye-based recordable DVD medium where a pit (mark) is formed by heat mode, pulse width and recording power of a series of recording pulses generated by laser emission on recording are optimized at a given recording velocity, and at a different recording linear velocity changes the state of formed marks or spaces. That is, the heat capacity of heating pulses needed for forming marks becomes insufficient; the average length of mark fluctuates because the temperature to be attained is different from that for an optimum decomposition temperature; or a uniform width of marks is not obtained because of change in the optimum duty ratio of heating pulses, and wider or narrower marks are produced depending on their length. These produce poor jitter performance.
Accordingly, in an optical recording medium compatible with recording from low linear velocity to high linear velocity, optimized recording conditions from a lowest linear velocity to a highest linear velocity are coded and recorded in advance in a stamper, and optimization in recording is attained at each linear velocity by using a substrate which is copied from the stamper.
However, with the advancement of high speed recording, particularly in CLV (constant linear velocity) recording, the rotation speed is too high at the innermost circumference, so that rotation at a highest linear velocity is sometimes disabled from the innermost circumference to a given position in radial direction. To meet this problem, recording is started at an attainable rotation speed at the innermost circumference, and when recording is done to the position in radial direction where recording at a highest linear velocity becomes attainable, the recording velocity is switched to the highest linear velocity. Upon switching the recording velocity, parameters of a recording strategy and a recording power are inevitably different from those used so far from the position of innermost circumference, so that recording is carried out under an optimum condition for the highest linear velocity. For the recording strategy, parameters coded in the medium can be used, but the recording power is often optimized at a value which deviates from the optimum value coded in accordance with the recording environment at that time. For example, after continuous recording job is performed for a given time, by heat generation of driving motors or LDs (laser diode) themselves, the temperature inside a writing drive is increased from the initial value when the writing job starts. With increase of the temperature inside, LD wavelengths shift to longer wavelengths. Particularly, a dye-based recording medium whose sensitivity shows wavelength-dependence suffers from a large effect, thereby deviation of the actual optimum recording power from a coded optimum power is liable to occur. Whenever an optimum recording power is deviated by shifting the LD wavelength to longer wavelengths, the optimum recording power almost always deviates in the direction of increasing its value.
Further, test-writing for optimizing a recording power at the position where the linear velocity is switched cannot be employed in view of continuity of data or reduction in data storage capacity.
When recording is carried out at a constant linear velocity without switching the recording linear velocity, it is needless to say that recording is started after power optimization is carried out using a power calibration area (power measuring area) at the innermost circumference. Further, test-writing (OPC: optimum power control) corresponding to multiple linear velocities is described in Japanese Patent Application Laid-Open (JP-A) Nos. 2000-163850, 2002-358642, 2003-016651, and others. For example, in JP-A No.2002-358642, there is described that an OPC zone (test-writing area) is provided on the high-speed recording side at the boundary of the recording area in each zone in ZCLV format. According to this invention, test-writing becomes possible at a recording velocity of each zone. However, correction of OPC is not described.
On the other hand, with recent speeding-up of velocity at which data are recorded in an optical disc, it sometimes happens that in the midst of recording data in an optical disc, the transferring velocity at which data to be recorded are transferred from a host computer becomes slower than the velocity at which the data are recorded in the optical disc. This status where data to be recorded run out is called buffer under-run. Recent optical disc devices are, in many cases, provided with a means for protecting recording called as “BURN-Proof” “Just link” or the like. With the help of this means for protecting recording, writing interrupts and holds its state for a while when buffer under-run comes up. After interruption, when the transferring velocity of data becomes large or data to be written are stored in sufficient quantity in a buffer memory, the interruption is unlocked and writing starts again. In this way, an optical disc is not wasted on the occasion of buffer under-run.
In the case of employing the above-mentioned means for protecting recording, in order to restart writing without fail at the address interrupted, it is required that the rotation of an optical disc and the timing of writing data be synchronized before writing starts again. In one synchronizing method used, the position of an optical pickup is relocated back to the address before the interrupted address and the data so far written are read at the same velocity as the one at which the data were written, and in this way, an EFM signal is obtained. On the other hand, another EFM signal on the writing side is generated inside an encoder; then, these two signals are combined and are used to get synchronization.
Examples of publicly known technologies on an optical recording medium which uses dye in its recording layer are listed as: in one example, a polymethine dye or a combination of a polymethine dye and a photo-stabilizing material is used for recording material; in another example, a recording layer comprises a layer containing a combination of a tetraazaporphyrin (porphyrazin) dye or a cyanine dye+an azo-metal chelate dye (salt forming dye) and a reflecting layer; in still another example, a combination of a formazan (metal chelate) dye + other dyes is used for recording material; and in still another example, a combination of a dipyrromethene (metal chelate) dye + other dyes is used for a recording material. They are too many to be listed here. Further, many examples are known where a dye is used for recording material which is subject to multi-pulse recording. However, to the knowledge of the present inventors, no document has been found which recognizes the importance of a power controlling method used in a linking stage where a recording velocity of a dye-based recordable DVD medium is switched to a highest linear recording velocity, or the importance of a recording waveform on high linear velocity recording.
It is an object of the present invention to provide a recording and reproducing method for a dye-based recordable DVD medium and an apparatus thereof wherein an excellent recording waveform is obtained on high linear velocity recording. Particularly it is an object of the present invention to provide a simple power controlling method used in a linking stage where a recording velocity for a recordable DVD medium compatible with high linear velocity is switched to a highest linear recording velocity.
Further, it is also an object of the present invention to provide a new method for formatting a recordable DVD system using a semiconductor laser which has an oscillation wavelength shorter than that for a CD medium system. The new method is an effective method in which unrecorded areas are eliminated from a data adding zone in the same manner as LPP (Land Pre-Pit) method. Also the new method is an excellent method in which no data error is produced by fine trimming of cutting width in the production of stampers or by leakage of LPP signals into a data zone, as compared with the DVD-R Land Pre-Pit method.